Method and means for regulating the sizing operation of an air classifier



March 7, 1961 H. JAGER 2,973,861: METHOD AND MEANS FOR REGULATING THE SIZING OPERATION OF AN AIR CLASSIFIER Filed April 13, 1959 United States Patent METHOD AND MEANS FOR REGULATING THE SIZING OPERATION OF AN AIR CLASSIFIER Heinz Jiiger, Bochum-Riemke, Germany, assignor to Westfalia Dinnendahl Groppel Aktiengesellschaft, Bochum, Germany, a corporation of Germany Filed Apr. 13, 1959, Ser. No. 805,984

3 Claims. (Cl. 209-1) tom used in the classifier for winnowing the fine material from the coarse residue. Such adjustment of the centrifugal system may be eifeoted manually when the classifier is at rest, or may be effected during operation of the classifier by regulating the speed of the motor driving the centrifugal system. However, before making any such regulatory adjustment, a test quantity of the separated fine material must be withdrawn and the amount of oversize grains must be determined. Heretofore, this manner of regulation for desired uniformity of the fines has been performed only intermittently with relatively long intermediate intervals of time during which the classifier may not operate satisfactorily.

It is an object of my invention to eliminate this disadvantage and to always secure obtaining separated fines of best possible uniformity.

To this end, and in accordance with a feature of my invention, I apply an automatic regulating method according to which a partial flow of the separated fines is tapped oil the classifier, and the proportion of oversize material in these fines is continuously determined, for example mechanically by sifting, or by optical means, or any other suitable manner, whereafter the quantity of the oversize material or a measuring instrument responding to that quantity is caused to impose a corresponding speed control upon the drive for the centrifugal fan or other driven classifier component whose speed determines the size range of the separated fines. In this manner a continuous adaptation of the classifying operation to the desired degree of uniformity of the separated fines is achieved.

According to another, less preferred feature of the invention the specimen quantity may be continuously taken from the material fed into the classifier, for controlling the size-determining speed of the drive.

The invention will be further described with reference to the embodiment of a driven centrifugal-type air classifier illustrated by way of example on the accompanying drawing by a vertical section of the classifier proper and a schematic diagram of its control components.

The material to be classified by air sizing is supplied into the hopper 2 of the classifier 1, as is schematically indicated by an arrow A. The material, containing a mixture of grains of various sizes, drops onto a' whirling disc 3 which is driven from a motor 3a. Due to the centrifugal action of the disc 3, the material is spread outwardly and is subjected to the centrifugal action of a fan system 4 whose vertical shaft 4a is driven through a belt transmission 4b and a speed-reducing transmission 5 from a motor 6. The coarse particles are flung outwardly against the peripheral inner wall 1a of the classifier and drop into the funnel-shaped bottom portion 1b of that wall whence they drain through an outlet conduit 10 as is. indicated by an arrow B.

The fines to be separately collected are blown upwardly and pass through a top opening 1d to an annular space 1e and into the funnel-shaped bottom portion 1f of the classifier housing from which they drain through a conduit 7. A fan 4c in the top portion of the structure fastened to the fan 4 and also driven from shaft 4a provides the required up-draft for drawing the fines through opening 1d.

Inserted into the flow of fines issuing from conduit 7, this flow being schematically represented by an arrow C, is a specimen receiver 8 which continuously collects a branched-off flow of material and passes it onto a test screen 9 or sifter, for example of the vibratory type. The proportion of fines within the permissible size limit is sifted oif through the screen, and all oversize particles are conveyed by the screen 9 down in the direction shown by arrow D onto an endless-belt type weighing scale 10 which is adjusted to the permissible amount, by weight, of the quantity of oversize material. Theendless belt rotates at constant speed so that the scale measures the oversize material by weight per time unit. When the amount being weighed passes above or below the adjusted limits, the movable beam of the weighing scale actuates one or the other of two electric contacts 11, 12 which control the drive motor 6 so as to either increase or de crease the rotating speed of the centrifugal system 4 as required for maintaining the degree of non-uniformity of the fines within the proper limits. As shown,;a recording measuring instrument 13 may be inserted into the control circuit of contacts 11, 12.

By virtue of the continuous withdrawal of a'sm'all specimen quantity from the flow of fines issuing from the classifier and the dependence of the driving speed upon the continuously measured value, a continuous supervi-' sion and regulation is achieved with the result o-falways maintaining the separated fines within the desired uniformity limits.

It will be obvious to those skilled in the art, upon a study of this disclosure, that my invention can be performed with the aid of apparatus other than specifically illustrated and described herein, without departing from the essential features of my invention and within the scope of the claims annexed hereto.

I claim:

1. An air classifying apparatus comprising a classifier having a centrifugal system whose speed determines the grain size of the fines being separated, said classifier having an outlet conduit for the separated fines and having a variable-speed drive connected with said system, a specimen receiver in the flow path of said outlet conduit for continuously withdrawing a specimen quantity of fines, said receiver having an overflow, a screening device mounted for continuously receiving material from said overflow and adapted to separate from "said material the component content of material beyond agivengrain size, an endless-belt weighing scale mounted to continuously receive said content from said receiving device and having a member movable in opposite directions from a balance position in response to departure of the Weight per time unit of said content from a given range, and speed control means connected with said drive and controlled by said member for accelerating and decelerating said centrifugal system in dependence upon said departure so as to maintain the grain size of the separated fines within a given range of uniformity.

2. Their classifying apparatus according to claim 1, said drive comprising an electric variable-speed motor having a speed-control circuit, and said movable member References Cited in the file of this patent UNITED STATES PATENTS Blomfield Mar. 15, 1927 Haglund June 3, 1958 

